Childhood lead poisoning is stated to be "the nation's leading childhood environmental disease" and being able to accurately determine toxic lead concentrations from small volumes of children's blood in an accurate and cost effective manner is a considerable challenge. This proposal describes a novel mercury fiber electrode that maintains the advantages of mercury as an electrode material and eliminates the problems associated with measurement in biological samples. This design places mercury inside a small diameter dialysis tube which can be directly dipped into a sample or it can be put in a flow stream for on line detection. The aims of this proposal is to characterize this electrode's performance; detection limits, precision and linearity of the lead ion response in the presence of interfering substances found in blood samples such as proteins and oxygen. The results of this research could lead to a portable, automated analyzer that could be used in the field or laboratory. In addition, many procedures have been developed using mercury electrodes and the analyzer could also be used to determine lead and other metals from environmental samples. The design also may have applications as a detector for liquid chromatographs for the determination of difficult to reduce substances.